Electrical prospecting apparatus



Oct. 2 5, T ZUSCHLAG' 1,884,496

ELECTRICAL PROSPECTING APPARATUS Filed lMay 3l. 1929 41, INVENTOR A Theodor Zusch/ag ATTORNEYS Patented er. 25, 1932 UNITED STATES PATENT OFFICE THEODOR ZUSCHLAG, OF NEW YORK, N.. Y., .ASSIGNOIB'` TO SWEDISH AMERICAN PROS- PECTING CORPORATION, OF NEW YORK, N. Y., .A CORPORATION 0F NEW YORK ELECTRICAL PROSPECTING APPARATUS Application led Hay 31, 1929. Serial No. 367,542.

y This invention relates to electrical prospecting apparatus. More particularly, it relates to alternating current prospecting apparatus, and has for its object the provision `g of improved apparatus of this character enabling the attainment of various new and improved results. It is well known that the nature of electrical or electromagnetic ground elds is deo pendent upon s uch geolectrical constants as the conductivity and permeability of the ground area in which the elds exist. In consequence systems of electrical prospecting have been developed wherein data on the geological structure of a given ground area is obtained by the systematic investigation of a ground field artificially induced in the area or the purpose.

In the systems of prospecting now in use,

n both alternating and direct current appara' tus are employed to generate' the ground ield. When direct current is used, the investigation of the ground field need be made only in respect to its magnitude or strength, '25 usually expressed as the amplitude of the E. M. F. induced by it in a searching coil. When alternating current is used, on the other hand, an investigation, to be complete, must, in addition to a1 determination of-the :i0 amplitude of the induced E. M. F., include also a determination of the phase relation between the exciter field, set up to induce the ground field, and the ground field itself. For practical reasons, the data on the amplitude and phase .is usually expressed as a function ofthe exciter field circuit, which therefore makes it necessary to establish some forni of relation or connecting link between the exciter fieldv circuit and the investigat- "ll, ing or search circuit.

The present invention concerns the provision of an improved form of alternating current prospecting apparatus wherein the exciter and search circuits are incorporated with a compensating or interconnecting circuit in such manner as to permit the determination of the amplitude of the E. M. F. induced by a ground field as well as the phase relation of `the ground field to the exciter field. Generally speaking, suchimproved ap- 5U paratus may be used in either potential or electromagnetic investigations and includes suitable means for determining the magnitude and phase relation'of the investigated ground field on the basis of the exciter circuit current.

More particularly, the present invention concerns the provision, in conjunction with exciter and Search circuits, of two alternating current generators coupled to one another and to a prime mover in such a manner that while both rotate at the same speed and generate E. M. F .s of equal value, the phase of the E. M. F. of one of them may be varied with respect to that of the other without causing any change in the amplitude of the two E. M. F.s. One of the generators is connected to the exciter circuit, such as exciter electrodes or an exciter loop, and the other generator isconnected through a potentiometer to the Search circuit, which may comprise search electrodes or a search coil or loop in series with a suitable indicating device.

Accordingly, with the apparatus connected as described, the establishment of an exciter field by the exciter circuit will result in the production of a ground field which will induce an E. M. F. in the search circuit. By means of the indicating device this induced E. M. F. can be observed, amplification being resorted to if necessary.

Through theinterposition of the potenti-` ometer between the search circuit and one of the generators, the induced E. M. F. in the search circuit can be balanced by deriving 4the proper value of E. M. F. necessary for balance from the E. M. F. of the enerator. If the induced E. M. F. and the alancing E. M. F. are ofthe same phase, which seldom is the case, phase adjustment of the generator v generator providing the balancing E. M. F.

' vided with an operating `can be ad]usted or varied until the two E. M. yF.s, the induced and balancing, are alike in phase as well as in amplitude, at which time the indicating device will indicate a balance. Both the amplitude and the phase displacement of the balancing E. M. F. can ,be readily determined and with this information the hase relation and amplitude of the E. 'M. of the investigated ground field ma be obtained.

In or er that the invention may be better understood, reference is made to the accompanying drawing, wherein:

Fig. 1 is a representation of apparatus in accordance with the invention.

`Fi 2 is a view in a lar er scale showing a deta' of the a paratus'o Fig. 1.

Fig. 3 is a etail view showing a modification of the construction shown in Fig. 2.

Considering the drawings more in detail, two identical alternating current generators 1 and 2, are coupled to one another at 3 and to a prime mover 4, such as a gasoline or electric motor. The output of generator 2 is connected through a non-inductive resistance 5 of known value and an `lammeter 6 to the switches 7 and 8, whereby connection with an exciter circuit constituted either by electrodes 9 and 10 or a loop 11 may be established.

The output of the generator 1 is connected across a potentiometer resistance 12. One end of the potentiometer, is connected to switch 13 andthe potentiometer slider is connected through an indicating device 14 to switch 15. By means of the; switches and 15, the potentiometer output\may be connected by leads 16 and 17 across the resi ance 5, as will be subsequently described, `or to a search circuit formed either by electrodes- 18 and 19 or search ,coil 20. l

As shown on anyenlarged scale in lFig. 2, the coupling devicet connecting the ltwo generators together, comprises coupling discs 21 and 22 each provided with a cylindrical hub 23, 24, having a cam slot`25 26 thereing, The hubs 23, 24 are axially slidable Von thel generator shafts, driving being effected through pins 27 28 mounted on the shafts and extend- 1n through the slots.

Ilngaging the discs 21, 22 alon their peripheries is a. guide block 29 carrie by a travelling nut 30 mounted on a screw 31 supported by suitable end bearinvs 32, 33 and proliandle or dial 34. To reduce friction between the peripheries of the discs and the guide block, ball bearings 35 may be provided. J

When the screw 31 is turned by means of the handle 34, the nut 30 is caused to move to ht or left carrying with it the guide the rig block 29. The discs 21, 22 w11.l thereby be forced to the right or left, and because of the pins 27, 28 projecting through the slots 25, 26,'such movement will cause the shafts to be angularly displaced with respect to one another. The rotors of the two generators accordingly will take on a. displaced relation,

and this results in a corresponding displace-V ment in the phase of their E. M. F.s.

Another arrangement whereby the phase of the two generators may be relatively varied is shown in Fig. 3. In this arrangement, the shafts of the generators 40, 41 are rigidly coupled to ether and to a prime mover 42 and one o the generators 41 is so mounted that its stator may be rotated about its axis g operation with the generator 2 connected to the exciter electrodes 9 and 10 and the generator 1 connected through the potentiometer 12 to the search coil 20, the indicating device 14 will show a pronouncedfdeflection due to the voltage drop across the portion of the potentiometer resistance 12 in the search circuit and also to the E.l M. F. induced in the search coil 20. By adjusting the potentiometer slider and turning the handle 34 of the coupling device 3, the indicating device can be restored to its zero position, at which point, the voltage drop is e ual to the induced E. M. F. and the voltage di generator 1 is in phase with the induced voltage.

Accordingly the value of theminduced voltage E2o may be expressed as where 1=current ilowinghe potentiometer a=potentiometer --"esista`nce between switchv 13 and the slider.

In the foregoing equation the induced voltage is expressed as a function of the current il. In practice, however, it is preferred to express the value of E20 in terms of the current flowing in the exciter circuit, in this case, the electrodes 9 and 10.

To obtain this relationship, the switches 13 and 15 are changed to connect the resistance 5 in circuit across the potentiometer instead of the search coil 20. The same operation of balancing the indicator to zero is then repeated.

The voltage drop Es across the resistance 5v canthen be expressed as;

where i2=current flowing inthe exciter circuit r5=value of the resistance 5 l=current owing through potentiometer I) potentiometer resistance between switch 13 and the slider.

From the foregoing equation the value of the current z'l can be expressed as,

Substituting this value of z', in the first equation:

when E20 will be expressed in terms of the exciter current 2. The value of f5 being known and constant as previously explained, the'values of a, i2 and b can be readily determined from the scale of the potentiometer and the scale of the ammeter and the value of E20 obtained.

In order to determine the phase displacement between theinduced E. M. F. and the exciter voltage it islonly necessary to subtract the readings of the dial 34, which, for practical purpose, may be graduated in degrees. Thus, if the dial reading for the first compensation or balancing operation was a1 and the dial reading `for the second balancing operation was a2, then the phase displacement p will be given as In the foregoing explanation, it has been pointed out that the exciter circuit was connected to electrodes and the search circuit to a loop. It is not necessary to the invention, however, that this arrangement be used. Each of the circuits may be connected to electrodes or to loops, or one may be connected to a loop and the other to electrodes; the apparatus is applicable equally as well to one form as to another.

1. Electricalprospecting apparatus comphase of the E. M. F induced ai the Search circuit by said artificial groundl field equals the E. M. F. supplied to said Search circuitv from said second source of alternating current.

4. In an electrical prospecting apparatus, the combination comprising an exciter circuit, a search circuit, two alternating current generators coupled to one another and to a prime mover so thatwhen both rotate at the same speed and generate E. M. F.s of equal v value to the phase of the E. M. F. of one of the generators may be varied with respect to the E. M. F. of the other without causing any change in amplitude of the two E. M. F.s.

prising an .exciter circuit for setting up an g artilicialground field, a source of alternating E. M. F. connected to said exciter circuit, a search circuit, a second source of alternating E. M. F. of the same frequency connected to said search circuit, said second source of alternating current being cou led mechanically. with said irst source of a ternating current in such a way that the phase of said second source may be varied in an arbitrary manner.-

2. Electrical prospecting apparatus according to claim 1, in which means are pro` vided for varying the value of the E. M. F. supplied bysaid second source of alternating E. M. F. to said search circuit.

3. Electrical prospecting apparatus f according to claim 1, in which means are provided for indicating when the value and the l (sul) CERTIFICATE 0F coRREcTloN. man No 1,884,496. october z5, '1932,

rnmbonfzuscmc.

-lt il' hereby certified tint 'error eppers in t above adored patent requiringy correction as follows: Page l, line 36, for 4,' strike out the word "to";

"circuit" rend "current"; page 3,'line 77, claim nl, tht the seid Lettere Patent should be read with these correctionsV therein that the enne my conform to the record of the case in the Patent Office.

Signed and sealed this 27th doy of December, A, Dit 1932.

he printed specification of the ming' cmissier of Inform.A 

